The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Optical recording devices are used to record information, such as music, movies, pictures, data, etc., on recordable media. Examples of recordable media are compact discs (CDs), digital versatile discs (DVDs), high density/high definition DVDs and Blu-ray Discs (BDs). In order to record such information, a recording device tracks the location of a laser beam on the recordable media.
Referring to FIGS. 1A-1B, a partial cross-sectional views of examples of recordable mediums 10-A, 10-B are illustrated. The recordable mediums 10-A, 10-B have lands 12 and grooves 14, which are formed on one or more recording layers 16 of one or more main substrates 18. The main substrates 18 may be adhered via an adhesive layer 20 to dummy substrates 22, as shown.
The lands 12 and grooves 14 refer to physical structures of the recording layer 16 that are adjacent each other but that have different associated depths. For example, the grooves 14 have a larger associated depth than the lands 12. Sample land depths D1 and sample groove depths D2 are shown. The depths may be measured relative to a disk outer surface 24 and are equal to a fraction of optical wavelength of the laser beam. The lands 12 and grooves 14 provide servo information for positioning of a laser beam spot on a disc. The lands 12 and grooves 14 also provide reflected beam signal modulation that is detected and used for tracking.
Standards, such as DVD+/−R and DVD+/−RW, require recording only over grooves. An alternative standard, referred to as DVD-RAM, requires recording over both land and groove structures. In DVD+/−R and DVD+/−RW recording, the lands 12 and grooves 14 typically form a continuous spiral. In DVD-RAM recording, the lands 12 alternate with the grooves 14 to form a continuous spiral.
Referring to FIG. 2, a sample optical DVD drive system 50 is illustrated that includes a laser source 52, such as a laser diode, that emits a laser beam 54. The laser source 52 may be part of an optical read/write assembly (ORW) 56. The ORW 56 includes a collimator lens 58, a polarizing beam splitter 60, a quarter wave plate 62, and an objective lens 64. The laser beam 54 is collimated by the collimator lens 58 and passed through the polarizing beam splitter 60. The laser beam 54 is received by the quarter wave plate 62 from the beam splitter 60 and is focused via the objective lens 64. The laser beam 54 may be radially displaced across tracks of the optical storage medium 68 through movement of the ORW 56 via a sled motor 66. The laser beam 54 is moved while the optical storage medium 68 is rotated about a spindle axis 69. The laser beam 54 is shaped and focused to form a spot over the land/groove structures of an optical storage medium 68 via lens actuators 70.
The light from the laser beam 54 reflects off the optical storage medium 68 and is thus directed back into the ORW 56. The reflected light, represented by dashed line 72, is redirected by the beam splitter 60. An astigmatic focus lens 76 focuses the reflected light into a spot over a photo-detector integrated circuit (PDIC) 74. Although not shown, additional photo-detectors may be used to detect other diffracted light beams, which are also not shown.